A team of researchers at Harvard University has tweaked bacteria and reengineered an artificial leaf to turn sunlight into the liquid fuel isopropanol.

Photosynthetic species including plants and algae have long harnessed sunlight as their direct source of energy. In an attempt to promote clean and renewable energy, humans have also invented photovoltaic cells capable of converting solar energy into electricity, as well as concentrated solar power that concentrates and redirects light and heat to drive steam turbine.

However, unlike plants and algae, the aforementioned human technologies are unable to efficiently and effectively store the converted energy. Both photovoltaic cells and concentrated solar power produce energy-on-demand. Harvard researchers have nonetheless come up with an innovative solution built on an earlier invention.

In 2011, chemist and Harvard professor Dr. David Nocera and his team introduced an artificial leaf capable of producing energy form sunlight and water. While this device mimics the ability of real leaves, it does not operate based on the concept of photosynthesis. The artificial leaf is actually a simple wafer of silicon coated in catalyst that breaks down water into its hydrogen and oxygen components upon exposure to sunlight. Nocera reintroduced the device in 2013, this time, giving it the ability to self-heal damage that occurs during energy production.

The device nonetheless received another improvement. Nocera realized there is almost no use tapping hydrogen as an energy source because the global society has grown dependent on liquid fuels. Thus, he collaborated with other researchers, including Harvard biologists, to revamp the artificial leaf using a reengineered Ralstonia eutropha bacterium capable of converting hydrogen into the liquid fuel isopropanol.

By using bacteria to convert solar energy into liquid fuel, the researchers have found an effective way to “store” the energy from the sun by converting it into an alcohol-based fuel.

The discovery is undeniably promising as it opens newer possibilities for harnessing energy from the sun. However, the entire concept is still in its infancy stage and researchers have a long way to go to achieve complete energy efficiency and of course, commercial viability.

Isopropanol is a colorless, flammable liquid. It is also known as isopropyl alcohol, 2-propanol, and propan-2-ol. It is a common household disinfectant. Moreover, its current use as an energy source only goes as far as being a fuel additive for automotive vehicles.

Further details of the findings are found in the article “Efficient solar-to-fuels production from a hybrid microbial–water-splitting catalyst system” published in 2015 in the journal Proceedings of the National Academy of Sciences.